A 22-year-old engineer from Reston has been charged in the slaying last weekend of a cabdriver in Tysons Corner after an anonymous tipster called Fairfax County police Sunday night and identified a suspect.

Someone saw the driver, Mazhar Nazir, 49, about 7 a.m. Sunday in his Dial Cab, which was parked near a garage in the 8400 block of Greensboro Drive. When the same person saw Nazir and the cab there six hours later, the person called police.

Nazir had been shot once in the head, court records say, and a 9mm shell casing was found in the cab. On Sunday night, police issued a news release calling it a "suspicious death." Later that night, Fairfax Officer Eddy Azcarate said, an anonymous caller identified a suspect: Evan D. Gargiulo, originally from New Jersey and living in an apartment off Baron Cameron Drive in Reston.

In a search warrant affidavit, homicide Detective John A. Wallace said that the victim's cellphone had been used to call a relative of Gargiulo's. On Tuesday, officers interviewed the anonymous caller and were told that Gargiulo had attended a Halloween party Saturday night wearing a wet suit, neoprene diver's boots and a blond wig.

Police searched Gargiulo's apartment, in the 1700 block of Port Place, on Tuesday afternoon, and found a wet suit and neoprene boots, court records say. Officers also found a 9mm handgun and two magazines for it, the search warrant says. The items were seized for testing.

Gargiulo, a systems engineer for Lockheed Martin in Reston, turned himself in at the Reston police district station at 5:30 p.m. Tuesday, police said. He was charged with one count of murder and one count of using a firearm in a felony. He was being held without bond last night at the Fairfax jail.

Azcarate said he did not know whether Nazir was robbed, but Gargiulo was not charged with robbery. Azcarate said he did not think there were any other witnesses.

Gargiulo graduated in the spring from Penn State University with a degree in information science and technology, said his attorney, Steven Garver. A Penn State Web site said Gargiulo coached the school's club swim team. Garver said Gargiulo was a lieutenant in the National Guard.

Garver described Gargiulo as "a really nice, good kid" who had not been in any previous trouble.

"It's just a horrible tragedy for everybody involved and their families," Garver said. "I'm sure if everybody could roll back the clocks, it probably wouldn't have happened." He declined to elaborate, saying that "eventually, the facts will come out."

Garver said he did not think anyone else was involved in the shooting. He said Gargiulo had given investigators "full cooperation."

Nazir had been driving for Dial Cab in the District for more than five months, said his manager, Abdul Khair. "Everybody liked him," Khair said, noting that co-workers had last seen Nazir on Saturday afternoon. "I can't believe it."

Nazir was married with a son. His body was being flown to his native Pakistan yesterday, acquaintances said. "He was a nice guy," said Jan Hamdullah, a neighbor in Nazir's apartment complex.